This invention pertains to the art of gear drive systems wherein a continuous rotary input on a drive gear results in an oscillating output of a driven gear. More particularly, the invention pertains to a gear drive system in which the driven gear is directly driven by the drive gear through one phase of its oscillating motion and driven in the reverse direction of oscillating motion through reverse cluster gearing driven by the drive gear.
Although the gear system of the present invention may have numerous applications including gears in an oscillating fan drive assembly, the system has particular use in an aircraft nosewheel steering system. In many aircraft steering systems, the steering motors are not capable of continuous rotation. The gear system of the present invention will permit such components that are not capable of continuous rotation to be coupled to a component that is capable of continuous rotation such as an airplane nosewheel.
Rotary to oscillating gear drive systems are known in the art as represented by U.S. Pat. No. 4,117,739. In the '739 patent, the drive gear includes two levels of gear teeth. Each level lacks an arcuate segment of gear teeth. As the drive gear is continuously rotated, the upper level of gear teeth will mesh with a first idler gear which in turn drives the output or driven gear. As the drive gear continues to rotate in the same direction, the drive gear will no longer drive the first idler gear due to the arcuate segment of missing gear teeth. Instead, the teeth located on the lower level of the drive gear will engage a second idler gear which in turn will drive the driven gear, through the first idler gear, in a reverse direction.
Providing the various levels of gear teeth on the drive gear in the '739 patent requires a gear of greater thickness and therefore increased weight. Furthermore, at each stage of engagement and disengagement between the drive gear and a respective idler wheel, potential gear jamming exists. No means are provided in the '739 patent to prevent gear jamming from occurring and thus the gear system is susceptible to teeth damage.
In an aircraft nosewheel steering system utilizing a motor which is not capable of continuous rotation, it is sometimes desirable to rotate the nosewheel through 360.degree. or more in maneuvering the aircraft. This is highly desirable in situations in which the aircraft has limited space in which to maneuver such as on an aircraft carrier. In the prior art systems, if the aircraft nosewheel is required to rotate greater than that permitted by the steering motor, the motor must be somehow disconnected from its drive train to the nosewheel. This requires an additional clutch or even disassembly of the drive system.
It is the object of present invention to provide a rotary to oscillating gear drive system wherein the output or driven gear is either directly driven by the drive gear in one direction or indirectly driven by the drive gear in a reverse direction through a reverse cluster gear arrangement. It is also the object of the present invention to provide a means to prevent gear jamming at times of coupling and decoupling of the drive gears. As applied to an aircraft nosewheel steering system, the present invention will permit continuous rotation of the aircraft nosewheel while oscillating the steering motor driven gear. This will prevent damage to the steering motor which would occur if the nosewheel was manually maneuvered beyond the permissible steering limits of the motor.